On a trip to a local primary school in South London earlier this month, prospective parents were somewhat surprised to find that a full 18% of the pupils were French.

This, the headmistress explained, was partly the result of an excellent French Lycée nearby (to which many of the pupils go on) and the tendency of expat communities to cluster in certain neighbourhoods.

But, even more surprisingly, the proportion of French children used to be higher: about 25% at the peak. So, why the drop (especially over a period when President François Hollande has been putting a squeeze on the wealthy and causing many to flee the country)?

The headmistress had a theory: it was because the French banks have been so dramatically “retrenching” (her word, I promise) in recent years.

London is, of course, far from being a one-industry town. But it can still come as a shock just how far and wide the City’s influence reaches beyond the Square Mile and the extent to which the fortunes of all its citizens are tied to the relatively small number of Londoners who work in its banks and investment firms.